Obstruction detector for a fluid flow line of a medical laboratory instrument

ABSTRACT

An apparatus for detecting obstructions of a flow line. A detector housing is provided having a cavity therein. The detector housing has first and second openings into the cavity. The flow line is attached to the detector housing establishing a flow path through the first opening, the cavity, and the second opening, respectively. A pressure detector detects changes in pressure within the cavity, indicating the presence of an obstruction.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for detecting obstructionsof a flow line, in particular, the fluid flow line of a medicalinstrument.

Automated sample handling systems are known that automatically aspiratepatient fluid samples, such as blood plasma, from sample tubes forsubsequent monitoring or testing of the fluid sample. For example, inU.S. Pat. No. 5,236,666 to Hulette et al., entitled "TemperatureRegulation in a Sample Handling System for an Optical MonitoringSystem," there is disclosed an automated sample handling system for anoptical evaluation instrument that can handle a high throughput ofpatient samples with a high degree of versatility, adaptability, andreliability. Hulette et al. discloses a sample handling system whichallows walk-away automation once sample tubes containing patient samplesare loaded into the system. The sample tube is automatically advanced toa piercer where a piercing probe is caused to pierce the septum of thesample tube. A sample probe is lowered a predetermined distance into thetube to aspirate a programmed amount of sample. The sample probe is thenremoved from the sample tube and the sample subsequently dispensed intoa cuvette.

Typically, the amount of fluid sample aspirated with automated samplinghandling systems is relatively small for example, 105 to 500microliters. Precise aspiration of the sample from the sample tube istherefore critical. Due to the micro-amounts of fluid being aspirated,relatively small obstructions within the fluid sample, such as bloodclots, can prevent the requisite amount of fluid from being drawn fromthe sample tube, resulting in inaccurate test results and decreasing theoverall efficiency of the system.

Precision microfluid pumps, such as Cavro brand pump, manufactured byCavro Scientific Instruments, Incorporated of Sunnyvale, Calif., havebeen developed that can accurately aspirate and dispense theaforementioned quantities. The Cavro brand pump is provided with asyringe having a plunger, and a stepper motor. To obtain the necessaryprecise volumetric delivery, the stepper motor moves the plunger acertain distance, for example, 0.0001 inch, aspirating an amount offluid proportional to the distance moved.

When a pump begins a normal aspiration cycle, there is associated withthis cycle within the fluid flow line an initial vacuum and a subsequentincrease in pressure. When the pump, for example, the aforementionedCavro brand pump, is turned on, the plunger within the pump is moved andbegins drawing a vacuum. As fluid is drawn into the fluid flow line, thefluid continues to move until the plunger of the pump stops. Because afluid in motion tends to stay in motion, when the moving fluid hits animmovable object, such as the piston, there is a resultant suddenpressure increase. However, if an obstruction, such as a blood clot,prevents the flow of the fluid within the flow line, this increase ofpressure is absent.

In the past, an operator or technician would typically manually checkthe sample tube for obstructions by holding the sample tube up to thelight and swishing the contents around while searching for foreignmaterial. However, this method requires human intervention, diminishingthe automation and flexibility of the aforementioned automated systems.Therefore, an automated device for detecting obstructions within a fluidflow line, minimizing human intervention, is desired.

The inventors experimented with an automated system of detectingobstructions in the fluid flow lines utilizing commercially availablepressure detectors placed within the flow line of the medicalinstrument, in between the aspirating probe and the corresponding pump.If a pressure increase at the end of the aspiration cycle was notdetected, this would indicate an obstruction of the fluid flow line,allowing the appropriate action to be taken. Stated alternatively, bymonitoring the pressure signal associated with the fluid flow line, thepresence or lack thereof of an obstruction could be determined.

It was discovered that the commercially available pressure detectorswere either too delicate or lacked the sensitivity for this application.The instantaneous pressures that were developed due to the pumpingaction of the microfluid pumps often exceeded the burst pressure of thecommercially available pressure sensors, causing them to break ormalfunction.

SUMMARY OF THE INVENTION

It is an object of the present invention to avoid the aforementioneddrawbacks by the provision of an obstruction detector having a durable,leak-proof housing through which the fluid sample flows.

It is a further object of the invention to provide the obstructiondetector with a reliable pressure sensor not subject to malfunction dueto pressure extremes for monitoring the pressure changes occurringwithin the housing.

It is yet another objective of the present invention to provide thedetector housing with an internal cavity that prevents the accumulationof bubbles within the detector.

The above and other objects are accomplished according to the inventionby the provision of an apparatus for detecting obstructions of a flowline including: a detector housing having a cavity therein, the detectorhousing having first and second openings into the cavity; means forattaching the flow line to the detector housing whereby a flow path isestablished through the first opening, the cavity, and the secondopening, respectively; and pressure detection means for detectingchanges in pressure within the cavity.

The invention will be described below in greater detail in connectionwith embodiments thereof that are illustrated in the drawing figures,where like reference numerals identify corresponding components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial elevation, showing internal structure in hiddenlines, of the present invention attached within a fluid flow line of amedical laboratory instrument.

FIG. 2 is an exploded plan view of the detector housing, and the sealingring.

FIG. 3 is a cross-sectional view of the detector housing along sectionalline 3-3 of FIG. 2.

FIG. 4 is a graphical representation of a normal aspiration cycle of afluid, illustrating a vacuum spike and a pressure pulse.

FIG. 5 is a graphical representation of an aspiration cycle of a fluidhaving an obstruction.

FIG. 6 is a graphical integration of the time rate of change of thepressure during a normal aspiration cycle.

FIG. 7 is a graphical integration of the time rate of change of thepressure during an obstructed aspiration cycle.

FIG. 8 is a view of a second embodiment of the present invention withtape disposed directly on the tubing.

FIG. 9 is a top view of the second embodiment illustrating the tubingand tape disposed on a bottom acrylic block.

FIG. 10 is a side view illustrating the tubing and tape disposed withintwo blocks.

FIG. 11 is a top view of one block.

FIG. 12 is a cross sectional view of the acrylic block.

FIG. 13 is a diagram of one example of the circuitry for connection tothe tape.

FIG. 14 is a graph of the rate of change of pressure over time.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a medical laboratory instrument 10 having a fluidflow line 12 is illustrated. Medical laboratory instrument 10 may be,for example, an automated sample handling device such as disclosed inU.S. Pat. No. 5,236,666 discussed above. Attached to one end 16 of fluidflow line 12 is a precision microfluid pump 18 such as a Cavro brandpump, manufactured by Cavro Scientific Instruments, Incorporated ofSunnyvale, California, that can accurately aspirate and dispenseprecision quantities of a fluid sample 20. Attached to the other end 22of fluid flow line 12 is a piercing probe 24. Piercing probe 24 iscaused to pierce the septum 26 of the sample tube 28 so that aprogrammed amount of fluid sample 20 contained within sample tube 28 canbe withdrawn.

Due to the micro-amounts of fluid being aspirated, relatively smallobstructions 30, such as blood clots, can prevent the requisite amountof fluid from being drawn from sample tube 28, resulting in inaccuratetest results and decreasing the overall efficiency of the system.

To detect obstructions 30, an obstruction detector 31 is placed withinfluid flow line 12 between ends 16 and 22. Obstruction detector 31includes a detector housing 32. Preferably, detector housing 32 has anessentially symmetrical, cylindrical shape, including a first end 34 andan oppositely located second end 36. Each end 34, 36 is further providedwith a concentric threaded female connector 41 for attaching fluid flowline 12 to detector housing 32. Female connectors 41 have respective,essentially concentric openings 38, 40, typically having a 0.05 inchdiameter. Fluid flow line 12 is severed and provided with a male flowline connector 42 at each severed end. Each male connector 42 isconnected to a respective female connector 41 of detector housing 32,thus establishing a fluid flow path from piercing probe 24, throughdetector housing 32, to pump 18.

Within detector housing 32 and between ends 34 and 36 is a cavity 43.Typically, cavity 43 has a first conically tapered region 44 adjacent toopening 38, a second conically tapered region 46 adjacent to opening 40,and a cylindrically shaped region 48 therebetween. Each tapered regiontapers outward towards cylindrically shaped region 48, for example, atan angle of inclination of about 23 degrees. It has been discovered thatif the angle of inclination is too steep, then micro bubbles flowingthrough fluid flow line 12 will attach themselves to the sloped taperedregion. Such bubbles tend to expand and contract with pressurefluctuations, interfering with the precision and accuracy of the system.

Typically, the diameter at the apex of each conically tapered regioncorresponds to the diameter of the respective opening 38, 40, and thebase diameter of each conically tapered region corresponds to thediameter of cylindrically shaped region 48, preferably 0.5 inch.Openings 38, 40 and cavity 43 establish a continuation of the flow pathof fluid flow line 12.

As illustrated in FIGS. 2 and 3, preferably detector housing 32comprises a first and a second portion 54, 56 connectable to each otherin an area corresponding to cavity 43. First portion 54 is provided witha concentric threaded female connection 58, and second portion 56 isprovided with a corresponding threaded male connection 60. First portion54 has a concentric o-ring groove 62 for receiving an o-ring 64 locatedat a base of female connection 58. Male connection 60 has a raised boss66 for contact with o-ring 64 when first and second portions 54, 56 arethreaded together. It has been discovered that the aforementionedarrangement results in a leak-proof detector housing that can beeconomically manufactured. Further, the placement of oring 64 and raisedboss 66 prevents the entrapment of air within the threaded connectionand the assembled detector housing.

Referring back to FIG. 1, a pressure detector 68 is provided fordetecting changes in pressure within cavity 43. Preferably, pressuredetector 68 comprises a piezo-electric tape, for example, Kynar Brandpiezo-electric tape, manufactured by Flexible Film Products Group, adivision of Amp Industries in Valley Forge, Pa., wrapped around theexterior of detector housing 32 in an area corresponding to cavity 43.Pressure detector 68 transmits a signal corresponding to the rate ofchange in the pressure within cavity 43 to a processor 70.

Typical operation of obstruction detector 31 in a medical laboratoryinstrument 10, such as the automated sample handling system disclosed inU.S. Pat. No. 5,236,666, is as follows.

Piezo-electric tape 68 is electrically connected to processor 70.Obstruction detector 31 is placed between pump 18 and piercing probe 24with the appropriate flow line connections being made, thus establishinga fluid flow path from pump 18, through first opening 38, cavity 43 andsecond opening 40, to piercing probe 24. Typically, to eliminate air,fluid flow line 12 and obstruction detector 31 are primed with a liquid,such as a wash buffer (not shown).

The sample tube septum 26 is pierced by piercing probe 24, beginning theaspiration cycle. The typical aspiration cycle causes an initial vacuumand a subsequent increase in pressure within fluid flow line 12. Whenpump 18, for example, the aforementioned Cavro pump, is turned on, aplunger (not shown) within the pump is moved and begins drawing avacuum. As fluid is drawn into fluid flow line 12, the fluid continuesto move until the plunger of the pump stops. Because a fluid in motiontends to stay in motion due to inertia, when the moving fluid hits animmovable object, such as the pump piston, there is a resultant suddenpressure increase. However, if an obstruction, such as a blood clot,prevents the flow of the fluid within the flow line, this increase inpressure is absent. By monitoring the pressure within the fluid flowpath, the presence or lack thereof of obstruction 30 can be determined,allowing the appropriate action to be taken.

Typically, pressure detector 68 is a piezo-electric tape wrapped aroundthe full circumference of detector housing 32 in an area correspondingto cylindrical shaped region 48 of cavity 43. The piezo-electric tapemeasures the microstrain of the detector housing, i.e., the expansionand contraction of the housing associated with pressure fluctuationsoccurring within cavity 43. Thus, because the sensitivity of thepressure detector is proportional to the amount of sensor area, byincreasing the diameter of cavity 43 in cylindrical shaped region 48,the sensitivity of the pressure detector is likewise increased.

The measured microstrain corresponds directly to the time rate of changeof the pressure within detector housing 32, i.e. the derivative of theactual pressure. As illustrated in FIG. 4, when there is no obstruction30 present, there is a distinct vacuum spike a and pressure pulse b.However, as FIG. 5 illustrates, when there is an obstruction present,the corresponding pressure pulse is either absent, or as illustrated atc, greatly reduced. Further, any pressure pulse that may be presentoccurs at a relatively later point in time, and is not as clearlydefined.

To further differentiate between a normal aspiration cycle and oneexperiencing an obstruction, the time rate of change of the pressurewithin detector housing 32, i.e. the derivative of the actual pressure,can be electrically integrated by processor 70 to convert the signal toactual pressure. As is illustrated in FIGS. 6 and 7, the integratedsignals received during a normal aspiration cycle is easilydistinguishable from the integrated signal received during an obstructedaspiration cycle. Once an obstruction is detected by obstructiondetector 31, processor 70 can take appropriate action.

As can be seen from FIG. 1, in the first embodiment of the presentinvention, a cavity is disposed at a point along tubing 12. In thesecond embodiment of the invention, tape can be applied to the tubingdirectly. As can be seen in FIG. 8, the tape, such as a film of polarpoly-vinylidene fluoride (PVF) is wrapped around small gauge tubing. ThePVF film, available, for example, from AMP Sensors (DTI-028K) is held inclose contact with the tubing by a block conforming to the shape of thetube. An electronic circuit is provided to amplify the signal from thefilm.

As can be seen in FIG. 8, tubing 12 is directly surrounded by tape 68.Wires 101 are connected to tape 68. Though illustrated in FIG. 8 aswrapping around the tubing, tape 68 could also be disposed along thetubing or in another arrangement where the tape will be compressed, aswill be discussed below.

As can be seen in a top view of the device in FIG. 9, the tubing 12 withtape 68 therearound, is placed on a block 110 having holes 105. As canbe seen in FIG. 10, a top block 110 is also provided. Each block has agroove 112 which corresponds to the tube 12 disposed therein.

As can be seen in top and side views of the acrylic blocks 110 (FIGS. 11and 12) holes 120 can be provided with screws 122 for securing the twoblocks together. Of course other means of securing the blocks would alsobe contemplated. In fact, any structural arrangement for the blockswhich would surround at least the portions of the tube 12 having tape 68thereon, would be envisioned.

As the pressure in the tube increases, such as when a clot blocks aprobe attached to tube 12, the walls of the tube expand. This expansionof tube 12 applies pressure to the PVF film. The film is pinched betweenthe expanding wall of the tubing and the rigid blocks surrounding thetubing and the film. The film produces a charge in direct proportion tothe rate of change of pressure within the tube. It is desirable for thechange in pressure to be greater than 8 PSI per second.

The PVF film produces small currents (in the nano Amp range). Leakage ofcurrent between the wires of the tape will weaken and distort thesignal. It is therefore desirable to use proper design techniques forthe electronics due to the small currents involved. FIG. 13 illustratesone example of circuitry connected to the film. The signal of the sensoris preferably amplified so as to aid in detection of rate of changes ofpressure within the tubing. FIG. 14 illustrates pressure changes overtime.

The invention now being fully described, it will be apparent to one ofordinary skill in the art that any changes and modifications can be madethereto without departing from the spirit or scope of the invention asset forth herein.

What is claimed is:
 1. An apparatus for detecting obstructions of a flowline, comprising:a flow line capable of allowing fluid to flowtherethrough; a pressure detector for detecting changes in pressurewithin said flow line, said pressure detector disposed on said flow lineor sufficiently proximate to said flow line so as to be compressed whensaid flow line expands; and a rigid barrier disposed proximate to saidpressure detector on a side of said pressure detector opposite said flowline, said rigid barrier being sufficiently rigid so that when said flowline and pressure detector expand, said rigid barrier does not expandand said pressure detector is compressed.
 2. The apparatus of claim 1,wherein said pressure detector is piezo-electric tape.
 3. The apparatusas defined in claim 2, wherein said piezo-electric tape comprises polarpoly-vinylidene fluoride.
 4. The apparatus according to claim 1, whereinsaid rigid barrier is at least one block disposed proximate to saidpressure detector.
 5. The apparatus according to claim 4, wherein saidat least one block is two blocks disposed in a face-to-facerelationship, wherein each face of each block comprises a groove forsaid flow line.
 6. The apparatus of claim 5, wherein said two blocks aremade of acrylic and are held together by screws.
 7. The apparatus ofclaim 2, wherein said piezo-electric tape produces a charge in directproportion to the rate of change of pressure within the tube when thepiezo-electric tape is compressed between the expanding wall of the flowline and the rigid barrier.
 8. The apparatus according to claim 7,wherein said pressure detector is capable of detecting a rate of changeof pressure of 8 PSI per second or more.
 9. The apparatus according toclaim 7, wherein said piezo-electric tape produces a signal whencompressed, which signal is amplified.
 10. The apparatus of claim 1,further comprising a probe connected at one end of said flow line. 11.The apparatus according to claim 10, further comprising an aspirationsource disposed within said flow line and in fluid communication withsaid probe.